1. Technical Field
The embodiments herein generally relate to Orthogonal Frequency Division Multiplexing (OFDM) receivers, and, more particularly to estimation of symbol boundaries using second order moment of the M-ary Phase Shift Keying (M-PSK) modulated pilots as the cost function in an OFDM receiver.
2. Description of the Related Art
In OFDM based systems the identification of a Fast Fourier Transform (FFT) boundary is a very important part of receiver symbol synchronization. Inaccurate or wrong detection of the FFT boundary may lead to phase errors in the payload carriers, which would lead to Bit Error Rate (BER) failures in the system, in the absence of suitable algorithms compensating for such phase errors. Typical OFDM system allocates some carriers to send known information for reducing the information carrying capacity of the system. These carriers are generally used for receiver synchronization and channel estimation.
One approach is using the Inverse Fast Fourier Transform (IFFT) of a channel estimate to get a symbol boundary for the system. This solution would require the pilot carriers to have the known information in turn reducing the payload of the system. Other approaches use the pilot phases for symbol synchronization which would only work when the symbol boundary is close to coarse symbol boundary. There are other schemes which use phase discontinuities on the pilots to determine the symbol boundaries.
FIG. 1 illustrates a block diagram depicting a portion of a typical OFDM receiver having a coarse symbol boundary detection block 102, a Fast Fourier Transformation (FET) window control block 104, a Fast Fourier Transformation (FFT) block 106, a carrier frequency (CF) and a sampling frequency (SF) offset estimation block 108, a channel estimation and correction block 110, a symbol boundary detection block 112, and a de-mapping and channel decoder block 112. Typically in OFDM receivers, symbol synchronization for OFDM system is done in two stages (i) Coarse Symbol Synchronization (CSS) and (ii) Fine Symbol Synchronization (FSS).
The coarse symbol synchronization uses the autocorrelation property of the OFDM symbol to determine the FFT window position which is controlled by the FFT window control block 104. With CSS (Coarse Symbol Synchronization), the FFT symbol boundary is within the guard interval of the OFDM symbol. Identification of the exact boundary of the FFT is an essential part of the OFDM systems because the OFDM signal is demodulated based on symbol structure whose arrival time is unknown. The wrong symbol synchronization would cause the Inter-Symbol Interference (ISI) resulting in an increase in Bit Error Rate (BER). Hence it is essential to achieve accurate and fast symbol synchronization for OFDM systems. All the above schemes require the information on the pilots to be known for determining the symbol boundary. Accordingly, there remains a need for receiver system and method for identifying the FFT boundary without the need for known information on the pilot carriers of the OFDM systems.